Aircraft and other structures built of composite materials may be inadvertently impacted by a service vehicle or other object without any external indications of the impact. Assessment of blunt impact to a composite material structure may be necessary or desirable to determine the necessity or feasibility of making repairs to the structure. Therefore, various methods used to assess the effect of blunt impact on a composite material structure have been devised.
Some techniques which have been used to assess the effect of blunt impact on composite material structures include the use of drop tubes, spring-actuated “guns” and pendulums. Drop tubes include relatively small masses (typically <100 pounds) which are dropped vertically through a tube onto a horizontal surface from a height which produces the desired energy level at impact. Spring-actuated guns use a spring to accelerate a small mass against a surface and can be used in any orientation. However, both of these techniques are limited to a small impact area (typically <˜12 square inches). Pendulums use larger masses and are used to perform impacts on vertical surfaces.
A drawback of conventional drop tubes and gun-type impact devices is that their relatively small masses and relatively high velocities do not replicate the damage which is sustained from large masses at relatively low velocities. Additionally, use of such devices may render acquisition of data during the impact difficult. Pendulums are generally much lower in mass than the vehicles that cause the impact which they attempt to replicate and typically cannot be used to reliably simulate impacts low on the body of an aircraft fuselage (particularly when an attempt is made to simulate a vehicle scraping under the belly or the cargo door of an aircraft). Pendulums may also require large or tall support structures; therefore, secondary impacts caused by such structures may be difficult if not impossible to prevent.
Using any of these conventional impact simulation methods on a complete aircraft in such a manner that the aircraft mass and moments of inertia are valid would be difficult at best. As an alternative, an actual service vehicle (or other powered vehicle with the appropriate bumper shape attached to it) may be used to impact the structure but such a solution would require that a human operator control the vehicle's velocity, direction and angle of impact, which would be unsafe and have poor repeatability. Elimination of the human operator factor in such a scenario would require a complex and expensive electronic control system or external thrust system.
Accordingly, a blunt impact test apparatus and method which can be used to test the effect of blunt impact having a measured magnitude on composite materials is needed.